Well Completion Apparatus, System and Method

ABSTRACT

An open-hole assembly for an open-hole section of a wellbore having a plurality of production intervals includes an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore, a plurality of isolation packers that provide zonal isolation between the open-hole wellbore and the outer tubing string, one or more screen assemblies positioned adjacent one or more of the plurality of production intervals, and a plurality of detectable references located along a length of the outer tubing string for registration of the completion assembly within the wellbore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to provisional U.S. Patent Application Ser. No. 61/587,196, filed Jan. 17, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

A. Field of the Invention

One or more embodiments disclosed herein relate to fracturing or gravel packing in subterranean wells. More particularly, one or more embodiments disclosed herein relate to registration within a wellbore of an open-hole completion assembly for fracturing and gravel packing and related methods of use.

B. Background and Summary of the Invention

In the drilling and completion of oil and gas wells, there usually are several oil and gas producing zones or regions in the formation traversed by the wellbore. Each producing zone may need to be separately fractured and subsequently gravel packed (also referred to as “frac-packing,” or “frac-pack”) to complete the well for oil and gas production. The expense and difficulty of assembling a drill string multiple times (i.e., making up a drill pipe string section by section) and proceeding thousands of feet into a well for each different producing zone of the well is costly and time consuming.

In light of the cost of proceeding with each producing zone independently and separately, it has been recognized that it may be an advantage to fracture and gravel pack 3 0 multiple zones without requiring multiple runs into the wellbore for each zone, such as by using specialized completion tool strings that have multi-zone fracturing and gravel packing capability.

As the application of single trip multi-zone frac-pack completions has progressed in, for example, the Lower Tertiary offshore in the Gulf of Mexico, it has become apparent that the multi-zone frac-pack completion concept may be applied to open hole completions as well as cased hole completions. As used herein, “open hole” completions refer to a well completion that has no casing or liner set across the reservoir formation, allowing the produced fluids to flow directly into the wellbore. “Cased hole” completions refer to a well completion that has a wellbore lined with a string of casing or liner. One benefit of applying multi-zone frac-pack completion techniques to open hole completions is the elimination of production casing across the reservoir interval and associated perforating operations, which are required after casing is installed for fluid production through the casing into the wellbore. It may be costly and time consuming to install production casing in a wellbore across the reservoir interval, and if that step can be avoided, and the well may be completed for production without casing across the reservoir interval, it may improve efficiency and lower completion costs.

In the design of apparatus and equipment for such multi-zone fracturing and gravel packing operations, it may be useful to avoid multiple “trips” into the wellbore. In wells that are thousands of feet deep, each additional trip into the wellbore requires a significant amount of rig time and effort to make up drill pipe in 30 foot sections (or greater) for thousands of feet of drill pipe. Each hour of rig time tripping into a wellbore is expensive. Furthermore, each trip introduces an additional opportunity for a problem or unexpected difficulty. Thus, it is a goal in the industry to reduce the amount of time and effort required to conduct completion operations.

A device and technique that is capable of installing a completion assembly with less time and effort, and with less trips into the wellbore, is desirable. This invention is directed to such an apparatus and technique.

In one aspect, embodiments disclosed herein relate to an open-hole assembly for an open-hole section of a wellbore having a plurality of production intervals, the completion assembly comprising (a) an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore; (b) a plurality of isolation packers that provide zonal isolation between the open-hole wellbore and the outer tubing string; (c) one or more screen assemblies positioned adjacent one or more of the plurality of production intervals; and (d) a plurality of detectable references located along a length of the outer tubing string for registration of the completion assembly within the wellbore.

In other aspects, embodiments disclosed herein relate to a method for multiple zone fracturing, packing and well treatment of an open hole section of a wellbore having casing positioned above the open hole section, the wellbore having a plurality of production zones, the method comprising (a) placing into an open hole section of the wellbore an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore, each portion of the outer tubing string being positioned adjacent one or a plurality of production intervals; and (b) registering a location of the outer tubing string with reference to the wellbore by a method being selected from one or both of the following: (i) a pipe tally reference, or (ii) a plurality of detectable references located along a length of the outer tubing string.

In yet other aspects, embodiments disclosed herein relate to an open-hole multiple zone fracturing, gravel packing and treatment completion assembly for single trip fracturing and packing operations of an open hole section of vertical, horizontal, or deviated wellbore having a plurality of production intervals, the completion assembly comprising (a) an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore; (b) a plurality of isolation packers that provide zonal isolation between the open-hole wellbore and the outer tubing string; (c) one or more screen assemblies positioned adjacent one or more of the plurality of production intervals; and (d) one or more radioactive detectable references in the cased section of the wellbore for registration with reference to the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of illustration and not limitation, the invention is described in detail hereinafter on the basis of the accompanying figures, in which:

FIG. 1 illustrates an offshore oil and gas platform operating an open hole completion apparatus in accordance with one or more embodiments of the present disclosure.

FIGS. 2A-2B illustrate cross-sectional views of an open hole completion assembly operating in a first zone of interest in accordance with one or more embodiments of the present disclosure.

FIGS. 3A-3B illustrate cross-sectional views of an open hole completion assembly operating in a second zone of interest in accordance with one or more embodiments of the present disclosure.

FIG. 4 illustrates an open hole single trip multi-zone completion assembly that is vertically registered in a wellbore in accordance with one or more embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The foregoing aspects, features, and advantages of the present invention will be further appreciated when considered with reference to the following description of the preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing embodiments of the invention illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the invention is not intended to be limited to the specific terms used, and it is to be understood that each specific term may include equivalents that operate in a similar manner to accomplish a similar purpose.

In the following description of the representative embodiments of the invention, directional terms, such as “above,” “below,” “upper,” “lower,” etc., are used for convenience in referring to the accompanying drawings. In general, “above,” “upper,” “upward” and similar terms refer to a direction toward the earth's surface along a wellbore, and “below,” “lower,” “downward” and similar terms refer to a direction away from the earth's surface along the wellbore. Additionally, the tee n “upstream” refers to a direction farther from the bottom or end of the wellbore, whether it be vertical, slanted, or horizontal; and the term “downstream” refers to a direction closer to the bottom or end of the wellbore, whether it be vertical, slanted, or horizontal.

One or more embodiments disclosed herein provides an apparatus and method for fracturing and gravel packing in an open hole section of a wellbore with only one trip into the wellbore being required. In the use of the invention, it is possible to register, at the correct location within the wellbore, the completion assembly with reference to the subterranean formation adjacent the wellbore without being required to take a preliminary trip into the wellbore for installing a lower packer (which has been used as an initial reference point or datum). “Registering” or “registration,” as used herein, means referencing and tracking a location of one or more components in relation to the adjacent wellbore or producing zones of the adjacent wellbore. In accordance with one or more embodiments, registration may be vertical (i.e., in a vertical wellbore), diagonal (i.e., in a slanted or diagonal wellbore), and/or horizontal (i.e., in a horizontal wellbore). Alternatively, registration may be performed in a wellbore having any combination or portions that are vertical, horizontal, deviated, or diagonal. As such, the technique of the invention does not require reliance upon a pre-positioned lower packer in the well. The technique of the invention does not require first positioning an open hole packer at a specific location in the lower portion of the uncased wellbore for an initial lower reference point or datum.

In yet other aspects, embodiments disclosed herein relate to an open-hole multiple zone fracturing, gravel packing and treatment completion assembly for single trip fracturing and packing operations of an open hole section of wellbore having a plurality of production intervals including an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore, a plurality of isolation packers that provide zonal isolation between the open-hole wellbore and the outer tubing string, one or more screen assemblies positioned adjacent one or more of the plurality of production intervals, and one or more detectable references such as formation response to electric line Gamma Ray in the cased section or open hole section of the wellbore for vertical, horizontal, or deviated registration with reference to the wellbore. Gamma ray formation logging is a measurement of the natural gamma rays emitted by various elements in the formation. Gamma ray logs are helpful for quantifying shaliness, well-to-well correlation, depth correlation between open- and cased-hole logs, and for correlation between logging runs.

Referring initially to FIG. 1, several open hole fracpack mechanisms that are deployed in an offshore oil or gas well are schematically illustrated and generally designated 10 in accordance with one or more embodiments of the present disclosure. One open hole fracpack mechanism used in accordance with one or more embodiments disclosed herein is available from Halliburton Energy Services, Inc. A semi-submersible platform 12 is centered over submerged oil and gas formation 14 located below sea floor 16. A subsea conduit 18 extends from deck 20 of platform 12 to wellhead installation 22, including blowout preventers 24. Platform 12 has a hoisting apparatus 26 and a derrick 28 for raising and lowering pipe strings, such as a substantially tubular, longitudinally extending work string referred to herein as an inner tubing string 30.

Importantly, even though FIG. 1 depicts a slanted well, it should be understood by one skilled in the art that the open hole fracpack mechanisms of the present invention are equally well-suited for use in vertical wells, horizontal wells, multilateral wells and the like. Also, even though FIG. 1 depicts an offshore operation, it should be understood by one skilled in the art that the open hole fracpack mechanisms of the present invention are equally well-suited for use in onshore operations.

Continuing with FIG. 1, a wellbore 32 extends through the various earth strata including formation 14. A casing 34 is cemented within a vertical section of wellbore 32 by cement 36. An upper end of a completion string, referred to herein as an outer tubing string 56 is secured to the lower end of casing 34 by a liner hanger 60 or other suitable support mechanism.

Note that, in this specification, the terms “liner” and “casing” are used interchangeably to describe tubular materials, which are used to form protective linings in wellbores. Liners and casings may be made from any material such as metals, plastics, composites, or the like, may be expanded or unexpanded as part of an installation procedure, and may be segmented or continuous. Additionally, it is not necessary for a liner or casing to be cemented in a wellbore. Any type of liner or casing may be used in keeping with the principles of the present invention.

Outer tubing string 56 may include one or more packers 44, 46, 48, 50 that provide zonal isolation for the production of hydrocarbons in certain zones of interest within wellbore 32. As used herein, “zonal isolation” may refer to isolated zones of the annulus between wellbore 32 and outer tubing string 56 fluidly isolated between one or more packers. When set, packers 44, 46, 48, 50 isolate zones of the annulus between wellbore 32 and outer tubing string 56. In this manner, formation fluids from formation 14 may enter the annulus between wellbore 32 and outer tubing string 56 in between packers 44, 46, between packers 46, 48, and between packers 48, 50. Additionally, fracpack and gravel pack slurries, also known as proppant slurries, may be pumped into the isolated zones provided therebetween.

In addition, outer tubing string 56 includes sand control screen assemblies 38, 40, 42 that are located near the lower end of tubing string 56 and substantially proximal to formation 14. As shown, packers 44, 46, 48, 50 may be located above and below each set of sand control screen assemblies 38, 40, 42.

Further, outer tubing string 56 includes closing sleeves 66, 68, 70 that provide a pathway such as a channel or an annular area that prevents proppant slurry from contacting the surface of formation 14 until the proppant slurry travels downhole to a desired location, such as near or proximal to one of screen control screen assemblies 38, 40, 42. The closing sleeves may be either shrouded or without a shroud more similar to that used in case hole operations. Preferably, closing sleeves 66, 68, 70 are each located in a zone of interest defined by packers 44, 46, 48, 50. In addition, outer tubing string 56 may include one or more open hole centralizers disposed along a length thereof.

It should be understood by those skilled in the art that the open hole fracpack mechanisms of the present invention may be used in a wellbore having any number of zones of interest. For example, FIG. 1 shows three zones of interest while FIGS. 2A-2B and 3A-3B show two zones of interest. Further, the open hole fracpack mechanisms of the present invention may be used in a wellbore having a single zone of interest if desired.

Referring now to FIG. 2A-2B and 3A-3B, detailed cross-sectional views of successive axial portions of open hole fracpack mechanism 80 are representatively illustrated. Outer tubing string 56 is secured to casing 34 with a liner hanger that is illustrated as a gravel pack packer 82. Gravel pack packer 82 includes slip assemblies and seals as well as other devices that are known to those skilled in the art for providing a sealing and gripping relationship between outer tubing string 56 and casing 34. Additionally, gravel pack packer 82 may be any type of packer, such as mechanical set, hydraulically set or hydrostatic set packers as well as swellable packers, for example.

An annulus 86 is formed between casing 34 and outer tubing string 56 that is sealed by gravel pack packer 82 at its upper or upstream end. Additionally, annulus 86 extends downwardly or downstream through the open hole of wellbore 32 and outer tubing string 56. Another annulus 88 is formed between outer tubing string 56 and a working string referred to herein as an inner tubing string 84. Inner tubing string 84 further includes an inner central passageway 100 for flowing a treatment fluid such as a fracpack or gravel pack fluid slurry referred to herein as a proppant slurry 90 to a particular zone of interest, as further described herein.

As shown, the present open hole fracpack mechanism 80 includes a shrouded closing sleeve 91. Shrouded closing sleeve 91 includes shroud 92, one or more frac ports 94 and a sliding sleeve 96. Shroud 92 is disposed concentrically about the outer surface of outer tubing string 56. Preferably, shroud 92 provides an annular region or other passageway or passageways, which is referred herein as channel 98, between the outer surface of outer tubing string 56 and the inner surface of shroud 92.

Frac ports 94 are disposed through outer tubing string 56, thus providing a passageway for proppant slurry 90 to flow into channel 98 of shroud 92. As can be seen, shroud 92 is attached, affixed, formed or may be integral with outer tubing string 56 just above or upstream of frac ports 94, thus providing a pathway for proppant slurry 90 to flow outward from frac ports 94, through channel 98 and downward or downstream to opening 154 of shroud 92.

Open hole fracpack mechanism 80 further includes a closing sleeve 96 that is slidably positioned or disposed between outer tubing string 56 and inner tubing string 84 such that it may be actuated to move relative to frac ports 94 for opening and closing the passageway provided by frac ports 94. As illustrated in FIG. 2A, frac ports 94 are shown in a closed position.

Open hole fracpack mechanism 80 further includes a sand control screen assembly 102 for filtering proppant from proppant slurry 90. Sand control screen assembly preferably includes a screen portion 104 and a base pipe 106 that may provide a channel 108 therebetween such that filtered fluid 148 is transmitted to one end of sand control screen assembly 102 where a valve 110 is located. The upstream or upper end of sand control screen assembly is shown located substantially proximal to opening 154 of shroud 92. As shown in FIG. 2A, valve 110 of sand control screen assembly 102 is in a closed position.

Open hole fracpack mechanism 80 also may include a pair of packers 111, 112 for sealing annulus 86 to provide zonal isolation. Alternatively, open hole fracpack mechanism 80 may be without packer 111 for a top completion interval, and instead cased hole packer 82 may provide the same function. Packers 111, 112 may be any type of packer commonly used and known by those skilled in the art.

In a lower portion of the illustrated open hole fracpack mechanism 80, as best seen in FIG. 2B, fracpack mechanism 80 includes a shrouded closing sleeve 119. Similar to shrouded closing sleeve 91, shrouded closing sleeve 119 includes shroud 120, one or more frac ports 118 and a sliding sleeve 122. Shroud 120 is disposed concentrically about the outer surface of outer tubing string 56. Preferably, shroud 120 provides an annular region or other passageway or passageways, which is referred herein as channel 152, between the outer surface of outer tubing string 56 and the inner surface of shroud 120.

Frac ports 118 are disposed through outer tubing string 56, thus providing a passageway for proppant slurry 90 to flow into channel 152 of shroud 120. As can be seen, shroud 120 is attached, affixed, formed or may be integral with outer tubing string 56 just above or upstream of frac ports 118, thus providing a pathway for proppant slurry 90 to flow outward from frac ports 118, through channel 152 and downward or downstream to opening 156 of shroud 120.

Closing sleeve 122 is slidably positioned or disposed between outer tubing string 56 and inner tubing string 84 such that it may be actuated to move relative to frac ports 118 for opening and closing the passageway provided by frac ports 118. As illustrated in FIG. 2B, frac ports 118 are shown in an open position.

Open hole fracpack mechanism 80 further includes a sand control screen assembly 128 for filtering proppant 150 from proppant slurry 90. Sand control screen assembly 128 preferably includes a screen portion 132 and a base pipe 130 that may provide a channel 131 therebetween such that filtered fluid 148 is transmitted to one end of sand control screen assembly 128 where a valve 134 is located. The upstream or upper end of sand control screen assembly 128 is shown located substantially proximal to opening 156 of shroud 120. As shown in FIG. 2B, valve 134 of sand control screen assembly 128 is in an open position.

Open hole fracpack mechanism 80 also includes a pair of packers 112, 136 for sealing annulus 86 and to provide zonal isolation. Packers 112, 136 may be any type of packer commonly used and known by those skilled in the art.

Open hole fracpack mechanism 80 includes a crossover assembly 114 positioned within inner tubing string 84. Crossover assembly 114 may be selectable to move fluids, such as proppant slurry 90 from inner central passageway 100 to annulus 88, for example. Crossover assembly 114 may also be selectable to move fluids from inner central passageway 100 to annulus 86 as further described below. Preferably, crossover assembly 114 is sealed against outer tubing string 56 by one or more seal elements 116 to provide a fluid tight engagement therebetween. In the illustrated embodiment, three seal elements 116 are shown; however, any number of seal elements may be used. In addition, open hole fracpack mechanism 80 includes one or more seal elements 146 slidably disposed between inner tubing string 84 and outer tubing string 56. In this manner, proppant slurry 90 flowing from crossover assembly 114 is forced through frac ports 118.

In FIG. 2B, crossover assembly 114 is shown substantially adjacent to frac ports 118 such that ports of crossover assembly 114 provides proppant slurry 90 from inner central passageway 100 through crossover assembly 114 to frac ports 118. As shown in FIG. 2B, closing sleeve 122 is in an open position, which enables proppant slurry 90 to cross through inner tubing string 84 and flow through frac ports 118 into channel 152 provided by shroud 120. Proppant slurry 90 then flows downstream or downwardly into the wellbore region surrounding sand control screen assembly 128. In the initial portions of the fracpack operation, a surface valve associated with annulus 88 may be closed or choked to prevent or limit fluid returns. As such, proppant slurry 90 is forced into formation 14 creating fractures 148, as best seen in FIG. 3B. Once the fracture stimulation portion of the treatment process is complete, the surface valve may be open such that fluid returns may be taken, as best seen in FIGS. 2A-2B.

As shown in FIG. 2B, inner tubing string 84 preferably has an open end 140 for receiving fluid 148. Fluid 148 may be conditioned drilling mud to control solids particle size and/or filtered solids-free completion fluid. As discussed further below, open end 140 may be provided after running inner tubing string 84 into wellbore 32 and then performing lifting operations on inner tubing string 84 to separate it from a plug 142 and a float shoe 141. Inner tubing string 84 may further include shifters 138 and 126 for opening and valves 110, 134 and closing sleeves 96, 122, respectively.

In another embodiment, inner tubing string 84 may have an open end 140 for receiving fluid 148 (either conditioned drilling mud to control solids particle size and/or filtered solids free completion fluid). As discussed further below, open end 140 may be provided after running inner tubing string 84 into the wellbore 32 and then performing lifting operations on inner tubing string 84 to close a sliding sleeve utilizing shifters above a bull plug (not shown).

The sliding sleeve may be covered or uncovered with well screen filter media. Inner tubing string 84 may further include shifters 138 and 126 for opening valves 110, 134 and closing sleeves 96, 122, respectively.

As noted above/open hole fracpack mechanism 80 may include any number of shrouds 92, 120 and they preferably include a portion that extends radially outwardly from outer tubing string 56. They may be sealed, formed, fastened, or otherwise affixed to the outer surface of outer tubing string 56 at a location that is proximal but upstream of frac ports 94, 118. As noted above, they may extend radially outward from this point where they are sealed or joined to outer tubing string 56. This radial extension may be substantially perpendicular or slanted relative to outer tubing string 56.

The longitudinal portion of shrouds 92, 120 extends from this point downwardly or downstream to a point that is substantially proximal to sand control screen assemblies 102, 128, respectively. The longitudinal portion of shrouds 92, 120 extend substantially parallel to wellbore 32 to a point where the openings 154, 156 are proximal to a zone of interest. For example, the zones of interest relative to FIG. 2A-2B are those portions of wellbore 32 that are substantially adjacent to sand control screen assemblies 102, 128. Shrouds 92, 120 provide a barrier that prevents proppant slurry 90 from contacting the surface of wellbore 32 prior to exiting openings 154, 156 in their respective zone of interest. By doing so they prevent proppant slurry 90 from dehydrating into formation 14 in a manner which may cause sand bridging at or near frac ports 94, 118 that may cause inner tubular 84 to become stuck in outer tubular 56.

It should be understood by those skilled in the art that the longitudinal portions of the shrouds of the present invention may be any length desired so long as they are of sufficient length to inject the proppant slurry to a location in the wellbore that is remote from the frac ports of the shrouded closing sleeves, i.e., a location in the wellbore sufficiently distant from the frac ports that dehydration of the proppant slurry does not occur at or near the frac ports. For example, the length of the longitudinal portions of shrouds of the present invention may extend for several sections of tubing making up the outer tubing string or may be only a few feet, depending on factors such as completion string configuration, formation characteristics, the type of proppant slurry to be pumped, the flow rate and pressure at which the proppant slurry will be delivered and the like.

Shrouds 92, 120 may be formed separately and then affixed to outer tubing string 56 prior to running it into wellbore 32. In another example, shrouds 92, 120 may be formed as a unitary part of outer tubing string 56. Generally, shrouds 92, 120 are of a substantially cylindrical shape reflecting the outer tubing string 56 in which they are disposed about. Preferably, they are thin-walled and made from a material, such as steel, that is sufficiently rigid to run into wellbore 32 along with outer tubing string 56 without becoming deformed.

In one embodiment, closing sleeves 96, 122 may be actuated by lifting or otherwise moving inner tubing string 84 upstream such that shifters actuate closing sleeves 96, 122. In another embodiment, closing sleeves 96, 122 may be actuated remotely by wired or wireless communication to a remote motor or actuator, for example.

Seal elements 116, 146 may consist of any suitable sealing element or elements, such as a packing stack with one or more O-rings either alone or in combination with backup rings and the like. In various embodiments, seal elements 116, 146 may comprise AFLAS.RTM. O-rings with PEEK back-ups, Viton®. O-rings, nitrile O-rings or hydrogenated nitrile O-rings or other suitable seal.

Referring collectively to FIGS. 2A-2B and 3A-3B the operation of open hole fracpack mechanism 80 will now be described. In the following, open hole fracpack mechanism 80 is being described in the context of a fracpacking operation, but as discussed further below, open hole fracpack mechanism 80 is also well suited for use in gravel packing operations and processes Open hole fracpack mechanism 80 is shown before and after fracpacking of a first zone of interest. In operation, open hole fracpack mechanism 80 of FIGS. 2A-2B may be run into wellbore 32 in a single trip or multiple trips on inner tubing string 84 and outer tubing string 56 to a desired depth. The gravel pack set packer 82 is then set against casing 34. In one embodiment, inner tubing string 84 and outer tubing string 56 are run into wellbore 32 with closing sleeve 96, valve 110, closing sleeve 122, and valve 134 in a closed position. Additionally, at this time packers 111, 112 and 136 may also be set by contacting them with a fluid to cause these packers to swell and seal against formation 14 of wellbore 32.

When inner tubing string 84 is initially run into wellbore 32, a float shoe 141 is attached to its lower end. In the illustrated embodiment, inner tubing string 84 may be attached to float shoe 141 using plug 142, which initially provides a seal in a profile 143 and is preferably coupled to float shoe 141 with pins or other suitable attachment members. After this assembly is positioned at the desired depth, outer tubing string 56 may be run to its desired depth and attached to the upper end of float shoe 141. Once in this configuration, a downward force on inner tubing string 84 may be used to shear the pins, thus freeing plug 142 from float shoe 141. Inner tubing string 84 may now move upwardly within outer tubing string 56. Preferably, inner tubing string 84 is moved upwardly to position plug 142 in the radially expanded region 144 of float shoe 142. In this position, fluid may be circulated through float shoe 141 as desired. Once packers 112 and 136 are set, inner tubing string 84 is moved upwardly to position plug 142 in profile 145 providing a seal therein. Further upward movement inner tubing string 84 releases plug 142, as best seen in FIG. 2B. By shearing inner tubing string 84 from plug 141, open end 140 is opened for receiving filtered fluid 148. Additionally, by setting plug 142 in profile 145, a sealed bottom environment is provided for preventing filtered fluid 148 from leaking off into formation 14 of wellbore 32.

In one embodiment, inner tubing string 84 may be further lifted or picked up further such that shifter 126 opens closing sleeve 122 and shifter 138 opens valve 134. Once these elements are opened, inner tubing string 84 may be lowered downstream to a position as best seen in FIGS. 2A-2B. In one embodiment, these lifting and lowering operations may operate or actuate crossover assembly 114 into a position to enable the fluid flow paths as shown in FIGS. 2A-2B.

During the lowering operation, seal elements 116 and seal elements 146 seal between inner tubing string 84 and outer tubing string 56. Proppant slurry 90 is then pumped down inner central passageway 100 to crossover assembly 114 where it crosses over to channel 152 via opened closing sleeve 122 and frac ports 118. Proppant slurry 90 then flows between shroud 120 and outer tubing string 56 as shown in FIG. 2B where it exits channel 152 at opening 156. After exiting opening 156, proppant slurry 90 then contacts formation 14 and, in one embodiment, fractures formation 14 through the use of a surface valve to prevent or limit fluid returns. During the fracture process, high pressure and high flow rate proppant slurry 90 is pumped into formation 14 creating fractures 148, as best seen in FIG. 3B. When it is desired to end the fracture portion of the fracpack, the surface valve is open to allow fluid returns.

The proppant 150 contained within proppant slurry 90 is now deposited or packed between formation 14 and sand control screen assembly 128, the results of which are depicted in FIG. 3B. The fluid portion of proppant slurry 90 is filtered through sand control screen assembly 128. Filtered fluid 148 then flows to opened port 134 where it exits and flows into annulus 88 and then toward open end 140 of inner tubing string 84. Filtered fluid 148 then flows up through inner central passageway 100 toward crossover assembly 114 where it crosses over to annulus 88 and then flows further upward or upstream where it may exit annulus 88 into annulus 86 via an exit port (not shown) located above gravel pack set packer 82, for example. This operation may continue until a desired amount of proppant 150 has been deposited or packed between sand control screen assembly 128 and formation 14, as best seen in FIG. 3B.

Once a first zone of interest has been treated, inner tubing string 84 may be picked up or lifted to the next zone of interest as best seen in FIGS. 3A-3B. Inner tubing string 84 is lifted such that shifter 126 and shifter 138 close closing sleeve 122 and valve 134 and open closing sleeve 96 and valve 110, respectively. The operations as discussed above may then be repeated to fracpack the second zone of interest. Specifically, proppant slurry 90 is then pumped down inner central passageway 100 to crossover assembly 114 where it crosses over to channel 98 via opened closing sleeve 96 and frac ports 94. Proppant slurry 90 then flows between shroud 92 and outer tubing string 56 as shown in FIG. 3A where it exits channel 98 at opening 154.

After exiting opening 154, proppant slurry 90 then contacts formation 14 and, in one embodiment, fractures formation 14 through the use of a surface valve to prevent or limit fluid returns. During the fracture process, high pressure and high flow rate proppant slurry 90 is pumped into formation 14 creating fractures. When it is desired to end the fracture portion of the fracpack, the surface valve is open to allow fluid returns.

The proppant contained within proppant slurry 90 is now deposited or packed between formation 14 and sand control screen assembly 102 (not shown). The fluid portion of proppant slurry 90 is filtered through sand control screen assembly 102. Filtered fluid 148 then flows to opened port 110 where it exits and flows into annulus 88 and then toward open end 140 of inner tubing string 84. Filtered fluid 148 then flows up through inner central passageway 100 toward crossover assembly 114 where it crosses over to annulus 88 and then flows further upward or upstream where it may exit annulus 88 into annulus 86 via an exit port (not shown) located above gravel pack set packer 82, for example. This operation may continue until a desired amount of proppant has been deposited or packed between sand control screen assembly 102 and formation 14.

In certain embodiments, a radioactive traceant may be disposed or mixed within the proppant so that when the proppant has been deposited or packed between the sand control screen assembly 102 and formation 14, a gamma ray tool will pick up the radioactive traceant in the proppant, and therefore may identify the producing zone. Environmentally friendly radioactive traceants may be mixed with the proppant. For example, radioactive elements such as iridium, scandium, and other radioactive elements approved by the EPA known to one of ordinary skill in the art may be used.

Although, the above operations have been described relative to a fracpacking operation, the present open hole fracpack mechanism 80 may be used in gravel packing operations as well. In one embodiment, shrouds 92, 120 direct proppant slurry 90 to substantially the top or upstream portion of sand control screen assembly 128 and sand control screen assembly 102, respectively, but fluid returns are allowed during the entire operation resulting in the packing of the wellbore regions surrounding sand control screen assembly 128 and sand control screen assembly 102 without fracturing the formation.

Referring to FIG. 4, a completion assembly 200 with one or more open hole fracpack mechanisms may be vertically registered in relation to the adjacent wellbore in accordance with one or more embodiments disclosed herein. FIG. 4 shows an open-hole multiple zone fracturing, gravel packing and treatment completion assembly 200 for single trip fracturing and packing operations of an open-hole section of a wellbore having a plurality of production intervals. The completion assembly 200 includes an outer tubing string having an upper end 202 adapted for connection with a lower end of a cased section of the wellbore, a plurality of isolation packers 208 that provide zonal isolation between the open-hole wellbore and the outer tubing string, one or more screen assemblies 206 positioned adjacent one of the plurality of production intervals 5, and a plurality of tags or markers 210 placed along a length of the outer tubing string that are detectable by a logging reference tool (not shown) for vertical registration of the completion assembly 200 within the wellbore.

For example, an accurate pipe tally (i.e., a length measurement) of the outer tubing string (i.e., workstring or drillpipe) may in many instances provide acceptable positioning for the completion assembly 200 in the wellbore. In other embodiments disclosed herein, vertical registration of the completion assembly 200 may be conducted by reference to locating radioactive tags or markers placed along a length of the drillstring or within the casing at or near the top of the completion assembly 200. Each of these techniques are further described herein.

Two primary depth references employed in the downhole (i.e., sub-surface) environment may be referred to as a “driller's depth” and a “logger's depth” (also called a wireline logger's depth). These two measurement systems may be recorded quite differently, although each may be used to verify or double-check the other. The driller's depth also is referred to herein as a “pipe tally.” The logger's depth may be referenced herein by the use of radioactive tags, PIP tags or “RA” tags, which are radioactive tags or markers in casing threads or perforations that can quickly and positively be found with a gamma ray logging tool, or other tools known to one of ordinary skill in the art.

In certain embodiments, detectable references (e.g., tags or markers) 210 may be disposed at intervals along a length of the outer tubing string. For example, detectable references 210 may be disposed along a length of the outer tubing string at every stand. As used herein, for example, a stand may be at least every 200 feet, every 220 feet, or every 240 feet, and up to every 260 feet, every 280 feet, or every 300 feet along a length of the outer tubing string. Alternatively, detectable references 210 may be disposed along a length of the outer tubing string at every other stand, or every third stand, or every fourth stand, and so on as determined by one of ordinary skill in the art. Still further, other spacing intervals may be used as will be understood by one of ordinary skill in the art. In addition, detectable references 210 may be evenly spaced or unevenly spaced along the length of outer tubing string.

In certain embodiments, the detectable references 210 may be disposed in threaded connections of the outer tubing string. For example, detectable references 210 may be a small wire strand that is inserted into the threaded connections prior to make up of each threaded connection. After make up of the threaded connection, the wire strand is captured between corresponding male and female threads and held in place. The wire may be any radioactive material that is detectable by gamma ray logging tools. For example, in certain embodiments, the wire strand may be cobalt, zinc-65 or other gamma ray emitting materials. Other methods of attachment may be used including, but not limited to, adhesives, welding, brazing, and other attachment methods known to one of ordinary skill in the art. A radioactive marker sub may also be run in-line with the workstring above the packer. The marker sub may serve as a tubing collar or drillpipe tool joint, with one or two small cavities drilled and threaded to receive a sealing plug. A radioactive pip tag may be installed in each cavity. As used herein, a pip tag is a weak gamma ray source (e.g., cobalt-60). All radioactive material is fully recovered when the string is pulled.

In other embodiments, a pipe tally or a driller's depth measurement may be used to vertically register the completion assembly in the wellbore. Driller's depth measurements may be associated with drilling operations and other closely associated activities such as logging while drilling (“LWD”), measurement while drilling (“MWD”) and coring. Driller's depth may be recorded on a well site, and may constitute the primary depth measurement while wells are being drilled unless it is later superseded by the depth from an open or cased-hole wireline log measurement. Driller's depth usually includes a unit of measurement (e.g., meter or feet), and a datum reference (i.e., the rig floor). In certain embodiments, measurements may be taken that account for stretching of the outer tubing string, as will be understood by one of ordinary skill in the art. For example, certain software available from Landmark, a Halliburton Energy Services, Inc. company, is often used to calculate and account for stretching when using driller's depth measurement. For instance, DecisionSpace—Well Engineering Software is one software that will calculate pipe stretch. The analysis capabilities allow assessment of forces based on surface parameters, fluid properties, pressures, and temperature, among other variables.

There are several parts of the drilling site to be considered while measuring, including the assembly of rotating parts that goes down the hole, which is a series of drill pipe connections and drill collars ending in a rotating bit. Optionally, there may be tools employed for logging while drilling as well. The length of all components in the drillstring is measured, and this gives the driller's depth at a given point in time. As more pipe is added, and the drilling deepens, this measurement is updated. The driller's depth is sometimes called the pipe tally because it includes as part of the measurement the “tally” or count of pipe lengths that have been employed in assembling the drill string.

The bulk of the drill string is drill pipe which has a nominal length of about 9.6 meters per pipe section, however, in reality, not all pipes are the same length. Steel pipe has a “male” connection at one end (called the pin) and a “female” connection at the other end (called the box), and as each section of pipe is lowered into the hole it is connected to the pipe preceding it by threading together the male and female components.

Methods of vertically registering the completion assembly in the wellbore may include one of the above methods (i.e., driller's depth or logger's depth), or both. In certain embodiments, the completion assembly may be located upon depth by pipe tally and then adjusted and/or confirmed by referencing with a gamma ray logging tool a radioactive emitting tag embedded at intervals along a length of the outer tubing string or in the casing above the upper end of the completion assembly. This latter reference location technique may be referred to as a completion assembly correlation through drillpipe. In addition, a radioactive tag or marker in the casing threads may be located and referenced with a gamma ray log in some embodiments of the invention.

It is possible in the practice of one or more embodiments disclosed herein to run with the completion assembly an open hole packer 204 at the bottom of the single trip completion system as shown in FIG. 4. The bottom isolation packer may provide isolation from fluids below 7. Thus, this bottom isolation packer 204 may isolate and form a bottom for the gravel pack at the end of the gravel pack or frac-pack treatment for the lower zone. In the practice of one or more embodiments disclosed herein, this bottom isolation packer 204 is not required to be pre-installed and need not be employed as a reference for positioning the multi-zone assembly in the open hole.

The frac-pack completion assembly may be positioned in the wellbore based upon a workstring pipe tally. For closer or redundant depth correlation, to serve as a check and confirmation of depth, the relative position of one or more radioactive tags located in the casing or in the completion assembly and in combination with the gamma ray open-hole log may be evaluated using electric line logging equipment, as previously described.

One or more embodiments disclosed herein for the multi-zone single trip completion assembly include a number of advantages. For instance, prior to running the completion assembly, an initial trip into the wellbore to run and set a bottom sump packer is not needed because vertical registration of the completion assembly does not require a bottom sump packer. Therefore, fewer trips, in fact a single trip, are needed to vertically register the completion assembly. In addition, vertical registration of the completion assembly using pipe tally and/or radioactive markers detected with a gamma ray logging tool is more accurate (in certain instances, to within about 20 feet or less). Still further, the completion assembly for open hole completion eliminates the need for casing across the completion interval, cementing, or casing perforations, which may be considered higher risk operations.

Although only exemplary embodiments are specifically illustrated and described herein, it will be appreciated that many modifications and variations of the process and apparatus described herein are possible in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the claimed subject matter. 

What is claimed is:
 1. An open-hole assembly for an open-hole section of a wellbore having a plurality of production intervals, the completion assembly comprising: (a) an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore; (b) a plurality of isolation packers that provide zonal isolation between the open-hole wellbore and the outer tubing string; (c) one or more screen assemblies positioned adjacent one or more of the plurality of production intervals; and (d) a plurality of detectable references located along a length of the outer tubing string for registration of the completion assembly within the wellbore.
 2. The completion assembly of claim 1, wherein the plurality of detectable references include radioactive elements.
 3. The completion assembly of claim 1, wherein the plurality of detectable references are PIP tags.
 4. The completion assembly of claim 1, wherein the plurality of detectable references are cobalt wire inserted between threaded connections of the outer tubing string.
 5. The completion assembly of claim 1, further comprising one or more detectable references located in the cased section of the wellbore.
 6. The completion assembly of claim 1, wherein the plurality of detectable references are located at every stand along a length of the outer tubing string.
 7. The completion assembly of claim 1, further comprising a setting packer that includes slip assemblies and seals for providing a seal and gripping relationship between the outer tubing string and the cased section of the wellbore.
 8. The completion assembly of claim 1, further comprising one or more shrouded or non-shrouded closing sleeves positioned proximate to the one or more screen assemblies.
 9. The completion assembly of claim 8, where the one or more shrouded closing sleeves each comprise: a shroud disposed concentrically about the outer surface of the outer tubing string; one or more fracturing ports disposed through the outer tubing string, thereby providing a passageway for treatment fluid to therethrough; and a sleeve slidably positioned between the outer tubing string and the inner tubing string such that it may be actuated to move relative to fracturing ports for opening and closing the passageway provided by fracturing ports.
 10. The completion assembly of claim 1, further comprising an inner tubing string having an inner central passageway for flowing a treatment fluid, wherein the inner tubing string extends within the outer tubing string and an annulus is formed therebetween.
 11. The completion assembly of claim 1, further comprising a pipe tally reference of the completion assembly within the wellbore.
 12. A method for multiple zone fracturing, packing and well treatment of an open hole section of a wellbore having casing positioned above the open hole section, the wellbore having a plurality of production zones, the method comprising: (a) placing into an open hole section of the wellbore an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore, each portion of the outer tubing string being positioned adjacent one or a plurality of production intervals; and (b) registering a location of the outer tubing string with reference to the wellbore by a method being selected from one or both of the following: (i) a pipe tally reference, or (ii) a plurality of detectable references located along a length of the outer tubing string.
 13. The method of claim 12, further comprising registering the location of the outer tubing string with reference to the wellbore with a logging tool reference to a detectable reference in the cased section of the wellbore.
 14. The method of claim 12, further comprising disposing radioactive traceant within a proppant deposited or packed between the outer tubing string and surrounding formation.
 15. The method of claim 12, wherein the plurality of detectable references are radioactive.
 16. The method of claim 12, further comprising inserting cobalt wire between threaded connections of the outer tubing string.
 17. The method of claim 12, further comprising correlating a position of the outer tubing string in relation to one or more radioactive PIP tags in the casing with a no-go sub or a radioactive mark sub disposed in the outer tubing string.
 18. An open-hole multiple zone fracturing, gravel packing and treatment completion assembly for single trip fracturing and packing operations of an open hole section of vertical, horizontal, or deviated wellbore having a plurality of production intervals, the completion assembly comprising: (a) an outer tubing string having an upper end adapted for connection with a lower end of a cased section of the wellbore; (b) a plurality of isolation packers that provide zonal isolation between the open-hole wellbore and the outer tubing string; (c) one or more screen assemblies positioned adjacent one or more of the plurality of production intervals; and (d) one or more radioactive detectable references in the cased section of the wellbore for registration with reference to the wellbore.
 19. The completion assembly of claim 18, wherein the one or more detectable references are PIP tags.
 20. The completion assembly of claim 18, wherein the registration of the completion assembly includes a pipe tally. 